Build a top-selling smart phone and a wildly popular marketplace for music and applications, and what do you get? Only a big target on your back. According to the Wall Street Journal, the latest challenge to Apple will come from Sony, which plans to market an iPad-like device, a new smart phone – a kind of "PSP phone" – and an expanded version of its Sony Online Service.

The timing is propitious. Sony CEO Howard Stringer has presided over a grim period in the company's history – Sony recently announced plans to shutter 10 manufacturing plants and lay off 8,000 workers. Meanwhile, sales of the new PSP Go – a sleek, stripped-down version of Sony's popular PSP video game system – have sagged.

Stringer sees salvation in pursuing a similar strategy to Apple: a centralized site for games and applications, and a full line of compatible gadgets. But as Chris Foresman of Ars Technica notes, "Sony needs new products that can move in significant numbers if Stringer's plan to tie products into its online media service is to succeed."

Enter a smartphone which will play PlayStation games and a device that one Sony source says will blur "distinctions among a netbook, an e-reader and a PSP."

Of course, Sony isn't the only company to put Apple in its crosshairs. Back in January, Amazon announced that it would open the Kindle e-reader to third-party applications, which would be sold through Amazon's website. The move was largely seen as a preemptive strike against the forthcoming iPad.

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